In the field of object measurement, three dimensional (3D) scanners are used to measure and collect point data related to the shape of an object. The collected data or “point cloud” can then be used to reconstruct by extrapolation a 3D model of the object. The 3D model may be used in a wide variety of applications, such as in a manufacturing setting for taking quality control measurements of manufactured parts and comparing the measurements to the theoretical CAD data. There are two general types or classes of 3D scanners: contact and non-contact.
Contact 3D scanners take point measurements of the object through physical touch using a probe end mounted to an articulating arm. A coordinate measuring machine (or CMM) is a common example of a contact 3D scanner. Contact 3D scanners, however, do pose some disadvantages. One disadvantage is that it requires contact with the object being scanned, which presents the potential to modify or damage it. This is significant when scanning pliable, delicate or valuable objects. The other disadvantage of contact scanners is that they are generally slow compared to the other scanning methods. Physically moving the articulating arm that the probe is mounted on can be slow and tedious.
There are generally two types of non-contact scanners: active and passive. Active scanners emit some form of radiation and detect its reflection in order to probe an object. Possible types of radiation used include light, ultrasound or x-ray. Passive scanners, on the other hand, do not emit any kind of radiation themselves. Instead, passive scanners rely on detecting reflected ambient radiation, typically in the visible light portion of the spectrum.
Photogrammetry is an example of a measuring technique utilizing a passive scanner in the form of a digital camera. In photogrammetry, the three-dimensional coordinates of points on the object are determined by measurements made in two or more photographic images taken from different positions. Common points are identified on each image. A line of sight or ray can then be constructed from the camera location to the point on the object. The intersection or triangulation of these rays determines the three-dimensional location of the point. Photogrammetry is particularly useful in extracting data relating to the position of points along the outer surface of the scanned object, but provides very limited information about the outer surface itself.
Laser surface scanning is well known for scanning the outer surface of the object. Laser scanners, or other similar surface scanners, are useful in providing data on the outer surface of the object, but are not well suited for extracting point or edge data from the object.
The shortcomings of these scanning methods can be overcome by combining the data provided by each, thereby gaining the advantages of both technologies. Thus, it remains desirable to provide a tool that facilitates combining the data from photogrammetric and surface scanning techniques and a method for the use of such a tool in the field.